Drive apparatus

ABSTRACT

A hydrostatic transaxle with a bypass mechanism is disclosed, the transaxle having a center section attached to a housing, an axial piston pump disposed on the center section and driven by an input shaft, and an axial piston motor disposed on the center section having a cylinder block engaged to a motor output shaft. The bypass actuation rod has a cam formed on a first end that engages a block lift member. When the bypass actuation rod is rotated, the cam causes two legs of the block lift member to engage the cylinder block on either side of the motor output shaft and cooperatively lift the cylinder block of the axial piston motor off of center section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/067,334, filed on Oct. 22, 2014. The content of thatapplication is fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

This application relates to a hydrostatic drive apparatus generally, andin particular, to a hydrostatic transaxle with a bypass mechanism and abrake mechanism. The transaxle is intended for use in driving a vehicleor other powered machine or apparatus.

SUMMARY OF THE INVENTION

An improved hydrostatic transaxle with a bypass mechanism and a brakemechanism is disclosed and described in detail herein. The transaxle canbe mounted on a vehicle or other powered machine or apparatus to providepropulsion in cooperation with a prime mover.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forthillustrative embodiments that are indicative of the various ways inwhich the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a transaxle inaccordance with the teachings herein.

FIG. 2 is a perspective view of a portion of the transaxle shown in FIG.1, with certain components removed for clarity.

FIG. 3 is a perspective view of the main housing of the transaxle ofFIG. 1.

FIG. 4 is a perspective view of the portion of the transaxle shown inFIG. 2, rotated 180° about the axis of a pump input shaft, withadditional components removed for clarity.

FIG. 5 is a perspective view of the portion of the transaxle shown inFIG. 4, with additional components removed for clarity.

FIG. 6 is a perspective view of the portion of the transaxle shown inFIG. 5, rotated 180° about the axis of a motor output shaft, withadditional components removed for clarity.

FIG. 7 is a perspective view of a portion of an alternate transaxlesimilar to the embodiment shown in FIG. 2, having alternate embodimentsof cradle bearings, a swash plate, an inner brake puck and an outerbrake puck.

FIG. 8 is a perspective view of another embodiment of a transaxle inaccordance with the teachings herein.

FIG. 9 is a perspective view of a portion of the transaxle shown in FIG.8, with certain components removed for clarity.

FIG. 10 is a bottom view of a portion of the transaxle shown in FIG. 8,with certain components removed for clarity.

FIG. 10A is another view of the portion of the transaxle as shown inFIG. 10, with additional components removed for clarity.

FIG. 11 is a top view of the portion of the transaxle shown in FIG. 10,rotated 90° about the axis of a pump input shaft, with additionalcomponents removed for clarity.

FIG. 12 is a perspective view of a portion of the transaxle shown inFIG. 8 with certain components removed for clarity.

FIG. 13 is an exploded perspective view of a filter assembly of atransaxle in accordance with the teachings herein depicting itscooperation with a pair of check valves.

FIG. 13A is an exploded perspective view of another embodiment of afilter assembly depicting its cooperation with an alternate pair ofcheck valves.

FIG. 14 is a side view of a vent assembly of a transaxle in accordancewith the teachings herein.

FIG. 15 is a cross-sectional view of the vent assembly shown in FIG. 14along the line 15-15.

FIG. 16 is an exploded perspective view of the vent assembly shown inFIG. 14.

FIG. 17 is a top view of another embodiment of a vent assembly.

FIG. 18 is a cross-sectional view of the vent assembly of FIG. 17 alongthe line 18-18.

FIG. 19 is a perspective view of the base of the vent assembly of FIG.17.

FIG. 20 is a perspective view of the cap of the vent assembly of FIG.17.

FIG. 21 is a perspective view of another embodiment of a transaxle inaccordance with the teachings herein.

FIG. 22 is a bottom view of a portion of the transaxle shown in FIG. 21,with certain components removed for clarity.

FIG. 23 is a perspective view of the differential assembly of thetransaxle shown in FIG. 21.

FIG. 24 is a partially-exploded, perspective view of the differentialassembly of FIG. 23, with certain components removed for clarity.

FIG. 25 is a partially-exploded, elevational view of the differentialassembly of FIG. 23, with certain components removed and the housingshown cut away for clarity.

FIG. 26 is another partially-exploded, elevational view of thedifferential assembly of FIG. 23, with certain components removed andthe housing shown cut away for clarity.

FIG. 27 is another partially-exploded, elevational view of thedifferential assembly of FIG. 23, with certain components removed andother components shown cut away for clarity.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies oneor more embodiments of the invention in accordance with its principles.This description is not provided to limit the invention to theembodiment(s) described herein, but rather to explain and teach theprinciples of the invention in order to enable one of ordinary skill inthe art to understand these principles and, with that understanding, beable to apply them to practice not only the embodiment(s) describedherein, but also any other embodiment that may come to mind inaccordance with these principles. The scope of the invention is intendedto cover all such embodiments that may fall within the scope of theappended claims, either literally or under the doctrine of equivalents.

It should be noted that in the description and drawings, like orsubstantially similar elements may be labeled with the same referencenumerals. However, sometimes these elements may be labeled withdiffering numbers or serial numbers in cases where such labelingfacilitates a more clear description. Additionally, the drawings setforth herein are not necessarily drawn to scale, and in some instancesproportions may have been exaggerated to more clearly depict certainfeatures. As stated above, this specification is intended to be taken asa whole and interpreted in accordance with the principles as taughtherein and understood by one of ordinary skill in the art.

FIG. 1 shows a first embodiment of a hydrostatic transaxle 120. Ahousing cover 123 is secured to a main housing 122 with fasteners 124.An axle 182 extends from main housing 122 and is supported in an axlehorn 122 a at an inner bearing or journal location 122 b and an outerbearing or bushing location 122 c. A pump input shaft 129 also extendsfrom main housing 122 and may have a pulley (not shown) fixed thereoncapable of receiving a drive belt (not shown). A prime mover (notshown), such as an internal combustion engine or an electric motor, cansupply motive force to the pump input shaft 129 of transaxle 120 bymeans of the belt and pulley combination. Transaxle 120 includes ablock-lift bypass mechanism 160 having a bypass actuator 161 with anintegrally-formed arm 161 a extending from main housing 122. A controlarm 136 that ultimately controls the rotational speed and direction ofaxle 182 is fixed to a trunnion arm 134 (depicted in FIGS. 2 and 4) thatalso extends from main housing 122.

FIGS. 2 to 5 depict a transmission 121 and a reduction gear set 180 oftransaxle 120. Transmission 121 includes an axial piston pump 130 whichhydraulically communicates with an axial piston motor 140 throughporting having two separate passageways (not shown) formed in a centersection 150. Center section 150 is secured in main housing 122 byfasteners 151. Pump input shaft 129 extends through an opening 135 b ina swash plate 135 to the exterior of main housing 122. Pump input shaft129 is rotatably supported in an input shaft bore 150 i of centersection 150 and is further supported by a bearing (not shown) seated inan input shaft opening 122 f of main housing 122. A pump cylinder block131 is engaged to pump input shaft 129. Pump cylinder block 131 has aset of pump pistons 131 a axially disposed therein and runs on a pumprunning surface 150 a of center section 150. Swash plate 135 controlsthe output of axial piston pump 130 in a known manner as a result of thearcuate motion of swash plate 135 when trunnion arm 134 is rotated bycontrol arm 136. Alternatively, as is known, trunnion arm 134 may berotated by other means, such as an electric actuator. This arcuatemotion of swash plate 135 changes the angle of a pump thrust bearing132, which is seated in swash plate 135, relative to the axial alignmentof pump pistons 131 a to impart reciprocal motion to pump pistons 131 awhen pump input shaft 129 and pump cylinder block 131 are rotationallydriven by a prime mover (not shown), generating hydraulic fluid flow ofvariable displacement between axial piston pump 130 and axial pistonmotor 140.

A pair of guide ribs 135 a formed on swash plate 135 engages a pair ofguide grooves 122 g formed in main housing 122 to guide the arcuatemovement of swash plate 135. Guide ribs 135 a also interface with a pairof notches 137 a formed in a cradle bearing 137 to capture and movecradle bearing 137 along with swash plate 135. Cradle bearing 137 is insliding contact with a cradle bearing mating surface 122 h formed inmain housing 122 to each side of guide grooves 122 g. Pump input shaft129 extends through an input shaft opening 137 b in cradle bearing 137.Input shaft opening 137 b is elongated similar to opening 135 b toprovide clearance around pump input shaft 129 when swash plate 135 ismoved within its range of motion. In the illustrated embodiment, thecenterlines of guide ribs 135 a and corresponding guide grooves 122 gall lie on a plane that intersects the rotational axis of pump inputshaft 129.

A motor cylinder block 141 of axial piston motor 140 has pistons 141 aaxially disposed therein and runs on a motor running surface 150 b,which generally lies perpendicular to pump running surface 150 a. Theflow of hydraulic fluid from axial piston pump 130 into pistons 141 acauses pistons 141 a to bear against a motor thrust bearing 142. Becausemotor thrust bearing 142 is positioned at a fixed angle relative to theaxial alignment of pistons 141 a adjacent a motor displacement surface122 m formed in main housing 122, motor cylinder block 141 is urged torotate. Motor cylinder block 141 is slidingly engaged to a motor outputshaft 145 at a motor shaft first end 145 a via splines or the like andcauses motor output shaft 145 to rotate. Reduction gear set 180 isengaged to motor output shaft 145 at a motor shaft second end 145 b andis driven thereby. Motor output shaft 145 is rotatably supported solelyby center section 150 in a cylindrical bore 150 j as shown in FIGS. 5and 6. Bearings or the like (not shown) can be employed in cylindricalbore 150 j if needed.

A hydraulic circuit exists between axial piston pump 130 and axialpiston motor 140 that is normally closed during operation of transaxle120 with the exception of make-up hydraulic fluid from a sump 115, whichcan enter the circuit through a valve opening 155 b formed in a threadedplug 155 of one of a set of check valves 153 installed in center section150 as shown in FIG. 6. Each check valve 153 contains a bleed passage155 c in threaded plug 155 to reduce the harshness or immediacy of thetransaxle's response to operator inputs at control arm 136, improvingthe ride quality of any vehicle equipped with transaxle 120. Checkvalves 153 communicate with the internal porting (not shown) of centersection 150 by allowing make-up hydraulic fluid to be drawn through thecheck valve 153 that communicates with the low pressure or suction sideof the hydraulic circuit, which may be one or the other of check valves153 depending upon the direction of fluid circulation between axialpiston pump 130 and axial piston motor 140, thereby compensating forfluid losses during operation. A filter, substantially similar to thefilter 356 depicted in FIG. 10, can be attached to center section 150 ina known manner to remove contaminants from the hydraulic fluid enteringthrough check valves 153, if needed, to extend the service life oftransaxle 120.

Reduction gear set 180 includes a pinion gear 185 shown in FIGS. 2 and 5supported on and driven by motor output shaft 145, a combination gear186 having an inner gear 186 a drivingly engaged to an outer gear 186 b,and a final drive gear 187. Combination gear 186 is supported on a jackshaft 188 that is supported at one end by center section 150. Jack shaft188 is supported at its opposite end at the housing joint by supportpockets 122 s and 123 a formed in main housing 122 and housing cover123, respectively. Final drive gear 187 is supported on and drives axle182.

Axle 182 is journalled in axle horn 122 a at inner bearing location 122b and is supported by an axle bushing 183 at outer bearing location 122c. As shown in FIG. 2, axle bushing 183 includes fluid grooves and,additionally, fluid grooves (not shown) are formed inside axle horn 122a through the journal area alongside axle 182 to allow sump fluiddistribution throughout axle horn 122 a, including lubrication of anaxle seal 181. Optionally, bearings or bushings or a combination ofknown bearing and bushing components can be used at inner bearinglocation 122 b and outer bearing location 122 c.

During assembly, axle 182 is installed through axle horn 122 a andthrough a splined hub 187 a of final drive gear 187 such that an innerend 182 a of axle 182 is positioned adjacent a thrust surface 122 dformed on main housing 122, as best shown in FIG. 3. Then, a C-clip 189is installed in a groove 182 b formed on axle 182. Although other typesof retaining clips other than C-clip 189 could be used in this assembly,C-clip 189 simply slides into groove 182 b and can therefore beinstalled without using a tool. Final drive gear 187 is then movedaxially along a set of splines 182 c of axle 182 (as depicted in FIG. 4)toward axle thrust surface 122 d so that C-clip 189 is nested andretained in a C-clip recess 187 b formed in splined hub 187 a.

Shown in FIG. 4, a gear spacer 184 is then installed between final drivegear 187 and main housing 122 adjacent the side of final drive gear 187opposite C-clip recess 187 b so that C-clip 189 remains nested andretained in C-clip recess 187 b. An extension 184 a of gear spacer 184engages a spacer anti-rotation feature 122 e depicted as a slot formedin main housing 122 to prevent rotation of gear spacer 184. Through thisarrangement of components, final drive gear 187 is properly positioned,axial movement of final drive gear 187 is restricted in both directions,axle 182 is retained in main housing 122, and axial movement of axle 182is restricted in both directions.

As shown in FIGS. 3 and 5, mating features formed on center section 150and main housing 122 ensure proper orientation of center section 150 atinstallation. Specifically, two alignment pockets 150 c formedconcentrically about a first and a second center section fasteneropening 150 d mate with two pilot bosses 122 i formed concentricallyabout threaded pockets 122 j to establish X-Y positioning of centersection 150 in main housing 122. Planar mating surfaces 150 n and 122 wof these same two alignment pockets 150 c and two pilot bosses 122 iestablish a Z axis position of center section 150. A third set of planarmating surfaces 150 k and 122 v, formed on center section 150 and mainhousing 122, respectively, add mounting stability and further establishthe Z axis position of center section 150 and ensure perpendicularity ofpump running surface 150 a to pump input shaft 129. Planar matingsurfaces 150 n and 150 k are formed on center section 150 parallel topump running surface 150 a. The Z axis in this description is an axisparallel to or equivalent to the rotational axis of pump input shaft129. A third center section fastener opening 150 h is formed throughplanar mating surface 150 k, and a mating threaded pocket 122 k isformed through planar mating surface 122 v. Three center sectionmounting fasteners 151 oriented parallel to the rotational axis of pumpinput shaft 129 are installed through two openings 150 d and one opening150 h to engage two threaded pockets 122 j and one threaded pocket 122k, respectively, to secure center section 150 to main housing 122.

Referring to FIGS. 3, 4, 5 and 6, block-lift bypass mechanism 160 allowsaxle 182 to freely rotate when hydrostatic transaxle 120 is not underpower. This allows an operator of a vehicle equipped with hydrostatictransaxle 120 to freely move the vehicle without powering it up, e.g.when servicing the vehicle. A bypass actuator 161, comprising a bypassarm 161 a and a bypass actuation rod 161 b, extends into main housing122 with bypass actuation rod 161 b oriented generally parallel to pumpinput shaft 129. As shown, bypass arm 161 a and bypass actuation rod 161b can be integrally formed portions of bypass actuator 161, though aseparate arm and rod combination (not shown) may also be used in a knownmanner. O-ring grooves 161 d and 161 e are formed on actuation rod 161 bto receive a retention O-ring 165 and a sealing O-ring 166,respectively. Sealing O-ring 166 prevents fluid leaks by sealing aroundactuation rod 161 b in a conventional manner in an opening 122 t formedin main housing 122. Retention O-ring 165 abuts an internal land 122 uformed on main housing 122 to prevent outward movement of bypassactuator 161, thereby retaining bypass actuator 161 in main housing 122.This dual O-ring configuration allows bypass actuation rod 161 b, withO-rings 165 and 166 installed thereon, to be inserted into main housing122 through opening 122 t. Upon insertion of bypass actuation rod 161 b,retention O-ring 165 immediately retains bypass actuator 161 when itpasses through opening 122 t, thereby enabling simple assembly.Optionally, one or both of O-rings 165 and 166 can be integrally formedfeatures of bypass actuation rod 161 b, thereby further simplifyingassembly.

Bypass actuation rod 161 b is rotatably supported at its inner end 161 jin a bypass rod pivot opening or cradle 150 g of center section 150 asshown in FIG. 6. A U-shaped block-lift member 163 comprises a firstblock-lift leg 163 a having a first formed end 163 d, a secondblock-lift leg 163 b having a second formed end 163 e, and a pivot rod163 c connecting first block-lift leg 163 a to second block-lift leg 163b. Motor running surface 150 b is somewhat smaller than the diameter ofmotor cylinder block 141 to permit block lift member 163, and inparticular block-lift leg 163 a and second block-lift leg 163 b, tocontact motor cylinder block 141 at opposite sides of motor runningsurface 150 b. Pivot rod 163 c of block-lift member 163 is rotatablydisposed in a pivot groove 150 e of center section 150. A cam form 161 con the inner end 161 j of actuation rod 161 b is positioned adjacent tofirst formed end 163 d; as illustrated in FIG. 6, block-lift bypassmechanism 160 is in a disengaged state. When bypass actuator 161 isrotated in either a clockwise or counterclockwise direction to initiateengagement of block-lift bypass mechanism 160, cam form 161 c bearsagainst first formed end 163 d, thereby forcing block-lift member 163 torotate about the axis of pivot rod 163 c. A set of retention projections163 f formed on each of formed ends 163 d and 163 e interface with apair of arcuate surfaces 150 f formed on center section 150 to guide therotation of block-lift member 163 while retaining pivot rod 163 c inpivot groove 150 e. When block-lift member 163 is rotated, first formedend 163 d, and second formed end 163 e cooperatively contact and liftmotor cylinder block 141 from motor running surface 150 b, breakinghydraulic fluid communication between motor pistons 141 a and fluidports 150 m formed in motor running surface 150, and thus breaking thefluid communication between pump 130 and motor 140. Thus, motor outputshaft 145, reduction gear set 180, and axle 182 are free to rotatewithout hydraulic resistance.

FIGS. 1, 2 and 3 best illustrate a brake mechanism 170. A brake shaft172 is rotationally supported and sealed in an opening 122 p formed inmain housing 122. When brake shaft 172 is rotated either clockwise orcounterclockwise, via corresponding rotation of a brake arm 171 from aninitial position to a rotated position, a cam form 172 a on brake shaft172 forces a brake puck 174 against a brake rotor 176, which is mountedon pinion gear 185. Cam form 172 a also acts as a slot to locate brakepuck 174 and prohibit movement of brake puck 174 in an axial directionalong the axis of rotation of brake shaft 172. Pinion gear 185 ismounted on motor shaft second end 145 b of motor output shaft 145. Asshown in FIG. 5, pinion gear 185 has a drive gear portion 185 a and abrake rotor mounting portion 185 b. Brake rotor 176 is slidingly mountedon brake rotor mounting portion 185 b of pinion gear 185. A second brakepuck 175 is disposed in main housing 122 between brake rotor 176 and athrust surface 122 r formed on main housing 122. Inner puck locators 122n and outer puck locators 122 q are formed on main housing 122 to helpguide and retain brake pucks 174 and 175, respectively. As brake shaft172 is rotated further, additional axial movement of brake puck 174forces brake rotor 176 into frictional engagement with brake puck 175 asbrake puck 175 is forced against thrust surface 122 r, thereby brakingmotor output shaft 145. Additionally, brake puck 175 and thrust surface122 r cooperatively serve as thrust elements for motor output shaft 145to limit the movement of motor output shaft 145 in a direction along itsrotational axis. As indicated in FIG. 1, a spring 173 is disposed aboutbrake shaft 172 between brake arm 171 and main housing 122, bearingagainst each to bias brake mechanism 170 to a disengaged state. Thebidirectional nature of brake mechanism 170 permits an external brakelinkage (not shown) to actuate brake mechanism 170 in either rotationaldirection.

An alternate brake puck embodiment is illustrated in FIG. 7. A brakeshaft 272 with brake pucks 274 and 275 are arranged approximately thesame as in the previously described configuration. When brake shaft 272is rotated clockwise or counterclockwise, frictional braking is appliedto brake rotor 176 as in previously described brake mechanism 170. Brakepucks 274 and 275, however, have a greater contact area with brake rotor176 for improved braking efficiency and lower heat generation.Additionally, ease-of-installation grooves 275 a and 275 b are providedon T-shaped brake puck 275. Groove 275 b provides clearance around motorshaft second end 145 b during assembly while groove 275 a engages aprojection (not shown) formed on the transaxle main housing (not shown)that guides brake puck 275 into position during assembly and thenproperly positions brake puck 275 in relation to motor shaft second end145 b when brake puck 275 is fully installed.

An alternate swash plate embodiment in the form of a swash plate 235 anda pair of clip-on cradle bearings 237 is also illustrated in FIG. 7.Pump input shaft 129 extends through an opening 235 b formed in swashplate 235. A pair of projections 235 c formed on swash plate 235 engagesa pair of openings 237 c formed on each cradle bearing 237 such thatcradle bearings 237 are locked in place on swash plate 235 to move alongwith swash plate 235. As in the first embodiment, the centerlines of apair of guide ribs 235 a and corresponding pair of guide grooves (notshown) formed in the transaxle main housing (not shown) all lie on aplane that intersects the rotational axis of pump input shaft 129.

FIGS. 8 through 12 depict an embodiment of a hydrostatic transaxle 320that varies from the previously described embodiments in terms of themanner in which its bypass actuation rod 361 b is retained in a mainhousing 322, and the manner in which its integral bypass arm 361 ainteracts with the main housing 322 to limit rotation of the bypassactuation rod 361 b. Hydrostatic transaxle 320 also varies from thepreviously described embodiments in terms of the interaction of its mainhousing 322 and housing cover 323, the retention of cradle bearings 337by its swash plate 335, a bushing retention feature (lip) 350 w formedin the motor running surface 350 b of its center section 350, additionalsupport for loads induced at its jack shaft 388, and the details of itsbrake mechanism 370. The remaining components of hydrostatic transaxle320 are substantially similar in form and function to those of thepreceding hydrostatic transaxle embodiments and will not be furtherdescribed herein.

Hydrostatic transaxle 320 comprises a housing cover 323 secured to amain housing 322 with fasteners 324. Integral locating pins 322 x formedalong the perimeter of main housing 322 interact with pin alignmentopenings 323 b formed in housing cover flange 323 c to minimize sealantsmearing during the joining of main housing 322 and housing cover 323.Unless otherwise described herein, main housing 322 and housing cover323 are substantially similar in form and function to main housing 122and housing cover 123, respectively. An axle 382 extends from mainhousing 322 and is supported in an axle horn 322 a at an inner bearingor journal location 322 b and an outer bearing or bushing location 322c. A pump input shaft 329 also extends from main housing 322 and mayhave a pulley (not shown) fixed thereon capable of receiving a drivebelt (not shown). A prime mover (not shown), such as an internalcombustion engine or an electric motor, can supply motive force to thepump input shaft 329 of transaxle 320 by means of the belt and pulleycombination. Transaxle 320 includes a block-lift bypass mechanism 360having a bypass actuator 361 with an integrally-formed arm 361 aextending from main housing 322. A control arm 336 that ultimatelycontrols the rotational speed and direction of axle 382 is fixed to atrunnion arm 334 (depicted in FIGS. 9 and 11) that also extends frommain housing 322.

Center section 350, shown in more detail in FIGS. 11 and 12, includes apump running surface 350 a and a motor running surface 350 b formed oncenter section 350 generally perpendicular to each other. An axialpiston pump 330 is disposed on the pump running surface 350 a. A pumpcylinder block 331 of axial piston pump 330 is engaged to and driven bypump input shaft 329. Pump cylinder block 331 has a set of pump pistons331 a axially disposed therein and runs on the pump running surface 350a of center section 350.

The interaction of the set of pump pistons 331 a with a pump thrustbearing 332 disposed in swash plate 335 to create hydraulic displacementin response to arcuate movement of the swash plate 335 is as previouslydescribed for axial piston pump 130 and will not be further detailedherein. Similarly, a pair of guide ribs 335 a formed on swash plate 335engages a pair of guide grooves 322 g formed in main housing 322 toguide the arcuate movement of swash plate 335 in the manner previouslydescribed for swash plates 135 and 235, respectively. Retention of eachof a pair of clip-on cradle bearings 337 on the external, arcuatesurface of swash plate 335 is accomplished through the interaction of apair of projections 335 c formed on swash plate 335 with a pair ofopenings 337 c formed at opposing ends of cradle bearing 337 in themanner previously described for swash plate 235. However, swash plate335 provides additional retention capability for the cradle bearing 337disposed adjacent trunnion arm 334 through use of a pair ofintegrally-formed tabs 335 d, as depicted in FIG. 11. As installed,cradle bearings 337 are placed in sliding contact with cradle bearingmating surfaces 322 h formed adjacent opposing sides of guide grooves322 g in main housing 322. Overall, guide ribs 335 a and thecorresponding guide grooves 322 g formed in main housing 322 each have acenterline that lies on a plane intersecting the rotational axis of pumpinput shaft 329.

A hydraulic motor 340 having an axial piston motor cylinder block 341 isdisposed on motor running surface 350 b. Motor cylinder block 341 has aset of pistons 341 a axially disposed therein. Axial piston motor 340 isin fluid communication with axial piston pump 330 via porting having twoseparate passageways (not shown) formed in center section 350 betweenpump running surface 350 a and motor running surface 350 b. The flow ofhydraulic fluid from axial piston pump 330 into pistons 341 a causespistons 341 a to bear against a motor thrust bearing 342. Because motorthrust bearing 342 is positioned at a fixed angle relative to the axialalignment of pistons 341 a adjacent a motor displacement surface 322 mformed in main housing 322, motor cylinder block 341 is urged to rotate.Motor cylinder block 341 is slidingly engaged to motor output shaft 345and causes motor output shaft 345 to rotate.

Motor output shaft 345 is rotationally supported in a cylindrical bore350 j of center section 350. A bushing retention lip 350 w is integrallyformed with motor running surface 350 b to restrain axial movement of abushing (not shown) pressed into cylindrical bore 350 j thatrotationally supports motor output shaft 345. At a first end (notshown), motor output shaft 345 is drivingly engaged to motor cylinderblock 341. At a second end 345 b, motor output shaft 345 engages piniongear 385 to drive reduction gear set 380 and axle 382 in the mannerpreviously described for reduction gear set 180 and axle 182,respectively, and will not be further detailed herein. Thus, thecombination of axial piston pump 330, axial piston motor 340 and centersection 350 forms a transmission 321 drivingly engaged to a reductiongear set 380 disposed in sump 315 that powers axle 382.

Referring to FIGS. 9, 10, 10A, and 11, center section 350 of transaxle320 is oriented and mounted in main housing 322 in a mannersubstantially similar to that of center section 150, with the additionof a fourth set of planar mating surfaces 350 q, 322 aa formed on centersection 350 and a strengthening rib 322 bb of main housing 322,respectively. These respective surfaces cooperate to bear loads inducedat the jack shaft pocket 350 r formed in center section 350 thatprovides support to jack shaft 388 at a first end. This fourth set ofplanar mating surfaces 350 q, 322 aa also cooperates to establish a Zaxis position, as defined below, of center section 350. It should benoted that jack shaft 388 is supported and captured at its second end bya pair of cooperating support pockets 322 s, 323 a formed in mainhousing 322 and housing cover 323, respectively, along the housingjoint.

In the manner previously detailed for center section 150, two alignmentpockets 350 c formed concentrically about a first and a second centersection fastener opening 350 d mate with two pilot bosses 322 i formedconcentrically about threaded pockets 322 j to establish X-Y positioningof center section 350 in main housing 322. The planar mating surfaces350 n, 322 w of these same two alignment pockets 350 c and two pilotbosses 322 i, respectively, establish a Z axis position of centersection 350. The Z axis in this description is an axis parallel to orequivalent to the rotational axis of pump input shaft 329. A third setof planar mating surfaces 350 k, 322 v formed on center section 350 andmain housing 322, respectively, add mounting stability and furtherestablish the Z axis position of center section 350. The planar matingsurfaces 350 n, 350 k are formed on center section 350 parallel to pumprunning surface 350 a, helping to ensure the perpendicularity of pumprunning surface 350 a relative to pump input shaft 329. A third centersection fastener opening 350 h is formed through planar mating surface350 k, and a corresponding threaded pocket 322 k is formed throughplanar mating surface 322 v. Three center section mounting fasteners 351oriented parallel to the rotational axis of pump input shaft 329 areinstalled through the center section fastener openings 350 d, 350 h toengage threaded pockets 322 j, 322 k, respectively, to secure centersection 350 to main housing 322.

Additional functionality imparted to center section 350 includes a pairof threaded check valve ports 350 s, a pair of filter pin locatingpockets 350 u, and a threaded filter screw pocket 350 t, all formed onthe side of center section 350 opposite pump running surface 350 a.Referring to FIGS. 10, 12, and 13, each check valve port 350 scommunicates with one of the two separate passageways (not shown) formedin center section 350 between pump running surface 350 a and motorrunning surface 350 b. A pair of check valves 353 is disposed in thepair of check valve ports 350 s to provide make-up hydraulic fluid tothe closed hydraulic loop between axial piston pump 330 and axial pistonmotor 340. Check valves 353 comprise a threaded plug 355 having a valveseat 355 a disposed about a first end of a valve opening 355 b thatpasses longitudinally through threaded plug 355 and has a hexagonal formfor use with a hex tool during installation of check valves 353 in checkvalve ports 350 s. These threaded plugs 355 may optionally have a bleedpassage (not shown) as described for check valves 153, depending on thedesired ride quality of any vehicle equipped with transaxle 320. A checkball 352 that interacts with valve seat 355 a is retained by a set offlexible ribs 354 a in cage 354 of check valve 353. Cage 354 can be madeof a flexible polymer such as glass filled nylon (e.g. a PA46 glassfilled nylon), permitting the check ball to be inserted through flexibleribs 354 a during assembly. An error proofing tab 354 a prevents cage354 from being installed in check valve port 350 s in a reverseorientation, as it acts to prevent installation of threaded plug 355when installed improperly.

An alternate embodiment of a check valve 553 is illustrated in FIG. 13A,wherein cage 554 is symmetrically designed to allow reversibleinstallation in check valve port 350 s of center section 350,eliminating the need for an error proofing tab. In the manner previouslydescribed for check valve 353, a check ball 552 is sized to sealinglyinteract with a valve seat 555 a disposed about a first end of a valveopening 555 b longitudinally formed in a threaded plug 555. Check ball552 may be pressed through either end of cage 554 to be retained thereinby a plurality of ribs 554 a, wherein the material composition of cage554 may be that of a flexible polymer such as a glass filled nylon.Threaded plug 555 may optionally have a bleed passage 555 c whosediameter may be varied to produce a desired ride quality in any vehicleequipped with transaxle 320. It should be noted that the longitudinallength of the combined components of check valves 353 and 553 will bethe same for purposes of installation in a given port, such as checkvalve port 350 s, whereby the relative lengths of their cages 354, 554and threaded plugs 355, 555 can differ, but are dimensioned to result inthe same overall length.

Referring again to FIGS. 10, 12 and 13, a filter 356 may be installed oncenter section 350 to remove contaminants from hydraulic fluid enteringthe closed hydraulic loop through one or the other of check valves 353.The check valve 353 in communication with the low pressure or suctionside of the closed hydraulic loop may permit make-up fluid to passthrough its valve opening 355 b as check ball 352 is displaced fromvalve seat 355 a by differential pressure on each side of check valve353. Filter 356 comprises a filter base 357 and a filter cover 358 whoserespective side walls are sealingly joined when fastener 359, in thisinstance a threaded screw, affixes filter 356 to center section 350 atthreaded filter screw pocket 350 t. A pair of filter locating pins 357 aintegrally-formed on filter base 357 mate with filter pin locatingpockets 350 u on center section 350 to properly align the openings 357 cformed on filter base 357 with each of the check valves 353 installed incenter section 350. A deformable lip 357 b surrounds each of theopenings 357 c to sealingly engage the external face of each valve plug355 when fastener 359 is properly torqued. As best shown in FIG. 10,filter cover 358 has a filter screen 358 b to permit the intake ofhydraulic fluid from sump 315 through check valves 353 and a reinforcedbridge structure 358 a to accept the loading of fastener 359 and alsodeflect the stream of high pressure hydraulic fluid escaping through anoptional bleed passage (not shown) in valve plug 355, protecting filterscreen 358 b from damage. A magnet 348 may be disposed in magnet pocket357 d to collect any fine metal shavings circulating in the hydraulicfluid to improve the service life of critical components of transaxle320.

An alternate embodiment of a filter 556 is depicted in FIG. 13A, whereinthe filter screen 557 d has been relocated to the filter base 557. Asaffixed to center section 350 in the manner previously described forfilter 356, filter screen 557 d is oriented at the top of filter 556,reducing the introduction of entrained air into the closed hydraulicloop of center section 350 and improving hydraulic efficiency. Filtercover 558 is now formed as a solid cover that sealingly engages filterbase 557 in the manner previously described for filter 356, and furtherprovides reinforcement to accept the loading of a fastener, such asfastener 359, and deflects the stream of high pressure hydraulic fluidescaping through an optional bleed passage 555 c in threaded plug 555.The form and function of a pair of filter locating pins 557 a and a pairof deformable lips 557 b surrounding each of the openings 557 c offilter base 557 is substantially similar to that of filter base 357 andwill not be further detailed herein. It should be noted that the filters356, 556 and check valves 353, 553 described herein can be alternatelypaired with each other to work in combination with center section 350.

Referring to FIGS. 8, 9, 11 and 12, transaxle 320 includes an alternateembodiment of a block-lift bypass mechanism 360 having a U-shapedblock-lift member 363 and a bypass actuator 361. Bypass mechanism 360functions in substantially the same manner previously described forbypass mechanism 160, but varies in terms of the means by which itsbypass actuation rod 361 b is retained in main housing 322, and themanner in which its bypass arm 361 a interacts with main housing 322 tolimit rotation of the bypass actuation rod 361 b.

Bypass mechanism 360 has block-lift member 363 moveably disposedadjacent motor cylinder block 341 and bypass actuator 361. Bypassactuator 361, including a bypass arm 361 a and a bypass actuation rod361 b, extends into main housing 322. In this embodiment, bypass arm 361a is integrally formed with bypass actuation rod 361 b, though it couldbe detachably joined thereto in a known manner, and bypass actuation rod361 b is oriented generally parallel to pump input shaft 329. A firstend 361 j of bypass actuation rod 361 b can be formed as a cam section361 c that permits bypass actuator 361 to be rotated in a clockwisedirection or a counterclockwise direction in actuating bypass mechanism360.

Bypass arm 361 a, which is formed to effect rotation of bypass actuationrod 361 b in cooperation with a mechanical linkage (not shown), includesone or more rotation stop tabs, 361 f and 361 i for example, which,along with the edges 361 g, 361 h of bypass arm 361, engage variousfeatures on main housing 322 to prevent over-rotation of bypassactuation rod 361 b. This ensures that the amount of block-lift achieved(i.e. hydraulic bypass) builds to a maximum when the stop tabs 361 f,3611 or edges 361 g, 361 h engage corresponding features on main housing322 to prevent an over-rotation condition where hydraulic resistance maystill be present in the closed hydraulic loop between hydraulic pump 330and hydraulic motor 340. Such resistance hinders manual movement of anunpowered vehicle equipped with transaxle 320. It is important to notethat as depicted in FIG. 8, transaxle 320 is a right-hand unit, meaningthat it would be mounted on the right-hand side of a vehicle with itsinput shaft 329 oriented toward the front of the vehicle.Correspondingly, a mirror-image left-hand unit (not shown), would bemounted on the left-hand side of a vehicle such that its input shaftwould also be oriented toward the front of the vehicle. Stop tab 361 flies below the plane of bypass arm 361 a to engage a boss 322 dd formedon main housing 322 that stop tab 361 i passes over duringcounterclockwise rotation of bypass actuator 361, as stop tab 361 i lieswithin the plane of bypass arm 361 a. During clockwise rotation,block-lift bypass is maximized when edge 361 g contacts input shaft boss322 z. Conversely, for a left-hand transaxle unit (not shown), stop tab361 i engages a housing boss somewhat taller than boss 322 dd duringclockwise rotation of bypass actuator 361, and edge 361 h contacts theinput shaft boss during counterclockwise rotation of bypass actuator361. Thus, bypass actuator 361 may be used in both right-hand andleft-hand transaxle units.

Bypass actuation rod 361 b is shown in FIG. 12 with first end 361 jrotatably supported in a bypass rod pivot opening or cradle 350 g formedin center section 350 and positioned adjacent block-lift member 363. Asecond end of the bypass actuation rod 361 b extends through a bypassactuation rod opening 322 t formed in main housing 322. An O-ring groove361 e is shown as formed on bypass actuation rod 361 b and structured toreceive a sealing O-ring (not shown). The sealing O-ring can aid in theprevention of fluid leaks by sealing around bypass actuation rod 361 bin a conventional manner in opening 322 t. In addition, one or moreretention tabs 361 d can be formed on bypass actuation rod 361 b, wherea pair of exemplary retention tabs 361 d is illustrated in FIG. 12, toprevent outward movement of bypass actuator 361, thereby retainingbypass actuation rod 361 b in main housing 322. Retention tabs 361 d areflexible in nature to compress during passage through opening 322 t andexpand after insertion into main housing 322, acting therein againstbypass actuator retention surface 322 u to ensure retention. The O-ringand retention tab configuration allows bypass actuation rod 361 b toeasily be inserted into main housing 322 through opening 322 t duringassembly.

In FIGS. 11 and 12, bypass mechanism 360 includes a block-lift member363 having a first block-lift leg 363 a with a first formed end 363 d, asecond block-lift leg 363 b with a second formed end 363 e, and a pivotrod 363 c connecting first block-lift leg 363 a to second block-lift leg363 b. Pivot rod 363 c of block-lift member 363 can be rotatablydisposed in a pivot groove 350 e formed on center section 350 and have alocating protrusion 363 g on pivot rod 363 c structured to engage a gapbetween locating or retention ribs 350 p on center section 350. Cam form361 c on the first end of bypass actuation rod 361 h is positionedadjacent to first formed end 363 d. Cam form 361 c of bypass actuationrod 361 can bear against first formed end 363 d of first block-lift leg363 a to force block-lift member 363 to rotate about an axis of pivotrod 363 c. A retention projection 363 f is formed on each of firstformed end 363 d and second formed end 363 e where each of retentionprojections 363 f interfaces with a corresponding surface 350 f formedon center section 350 to retain pivot rod 363 c in pivot groove 350 e.Corresponding surface 350 f of various embodiments can be an arcuatesurface. Block-lift member 363 straddles motor output shaft 345 andcontacts motor cylinder block 341 in multiple locations when liftingmotor cylinder block 341 from motor running surface 350 b.

As illustrated in FIG. 12, block-lift bypass mechanism 360 is in adisengaged state. Rotation of bypass actuation rod 361 b causesblock-lift member 363 to contact motor cylinder block 341 in at leasttwo places to thereby lift motor cylinder block 341 away from motorrunning surface 350 b. When bypass actuator 361 is rotated in either aclockwise or counterclockwise direction to initiate engagement ofblock-lift bypass mechanism 360, cam form 361 c bears against firstformed end 363 d, thereby forcing block-lift member 363 to rotate aboutthe axis of pivot rod 363 c. Retention projections 363 f formed on eachof formed ends 363 d and 363 e interface with corresponding surfaces 350f formed on center section 350 to guide the rotation of block-liftmember 363 while retaining pivot rod 363 c in pivot groove 350 e. Whenblock-lift member 363 is rotated, first formed end 363 d and secondformed end 363 e cooperatively contact and lift motor cylinder block 341from motor running surface 350 b. Formed ends 363 d, 363 e and theirrespective block-lift legs 363 a, 363 b form gradual curves along theirlengths to ensure that contact with motor cylinder block 341 occurs onboth sides of motor cylinder block 341 near a line that bisects motoroutput shaft 345 and lies parallel to the axis of pivot rod 363 c,reducing wear on components by lifting motor cylinder block 341 in anaxial direction with respect to the axis of motor output shaft 345. Thislift breaks hydraulic fluid communication between motor pistons 341 aand a set of fluid ports 350 m formed in motor running surface 350 h;and more generically, it breaks the fluid communication between axialpiston pump 330 and axial piston motor 340. Thus, motor output shaft345, reduction gear set 380, and axle 382 are free to rotate withouthydraulic resistance.

The brake mechanism 370 of transaxle 320, as illustrated in FIGS. 8, 9,10 and 10 a, has substantially similar form and function to thepreviously described brake mechanism embodiments, particularly that ofFIG. 7, but comprises additional error-proofing features provided forits outer puck 375 and a revised brake arm 371 and brake shaft 372engagement. As compared to outer puck 275, outer puck 375 of the presentembodiment has an additional groove 375 c for error-proofing purposesduring installation. Grooves 375 a and 375 c cooperate with a pair ofprojections 322 y formed on main housing 322 to ensure properorientation of outer puck 375 during assembly of transaxle 320. Itshould be understood that a plurality of corresponding grooves andprojections can be utilized for this purpose. Clearance around thesecond end 345 b of motor output shaft 345 is provided by a groove 375 bon the opposite face of outer puck 375 from grooves 375 a and 375 c. Apair of outer puck locators 322 q formed on main housing 322 help guideand retain outer brake puck 375, along with a thrust surface 322 rformed on main housing 322. Unlike the inner puck locators 122 n ofbrake mechanism 170 (a pair of projections), the additional width ofinner puck 374 is accommodated by inner puck locators 322 n (a tab andan inner housing wall of main housing 322).

As compared to the engagement means of brake arm 171 and brake shaft172, wherein a roll pin 177 or the like not only retains brake arm 171on brake shaft 172, but also bears the torque load associated withactuating brake mechanism 170, the external end of brake shaft 372 isformed with a single D-shaped cross-section 372 b to more robustlyengage a brake arm 371, which has a corresponding single D-shapedopening 371 a. A fastener, such as exemplary rivet 377, merely retainsbrake arm 371 on brake shaft 372 and prevents axial movement along theaxis of brake shaft 372. The torque load associated with actuating brakemechanism 370 is borne by the single D-shape engagement. The biasing ofbrake mechanism 370 to a disengaged state by a spring, such as torsionspring 373, is as previously described for brake mechanism 170 and willnot further be described herein. Similarly, the function of brakemechanism 370 through use of a brake rotor 376 slidingly disposed abouta pinion gear 385 and further disposed between and selectively engagedby an inner puck 374 and an outer puck 375 upon rotation of a brakeshaft 372 having a cam form 372 a on the end proximate to inner puck374, which also serves to retain inner puck 374, is as previouslydescribed for brake mechanism 170 and will not be further detailedherein.

As shown in FIGS. 8, 10 and 10A, transaxle 320 is outfitted with a ventassembly 325 located in a threaded port 322 cc formed at or near thehighest point of main housing 322. Referring to FIGS. 14, 15 and 16,vent assembly 325 has a flow path formed through it to prevent thebuildup of case pressure in transaxle 320 as the temperature of itshydraulic fluid increases under operating conditions, venting trappedair and in extreme cases, expanded hydraulic fluid, to protect theintegrity of various shaft seals found in transaxle 320. A correspondingfunction of vent assembly 325 is to prevent the intrusion of water andother contaminants, as can occur during washing of a vehicle equippedwith transaxle 320. Vent assembly 325 includes a main body 326, a valve327, and a vent cap 328.

Vent cap 328 is generally formed as a flattened dome, though otherexternal shapes can be suitable. A spray shield 328 b is shown extendingfrom the internal surface of vent cap 328 to form a circular wall. Alocking groove 328 a is formed near the periphery of the internalsurface of vent cap 328.

Main body 326 is generally formed as a cylindrical fitting having anexternally threaded lower portion 326 b and a tool form upper portion326 a radially disposed about a valve seat 326 e to form an open centercavity 326 p. A primary passage 326 c runs throughout the length of mainbody 326, and a downwardly sloped flange 326 i extends radially aboutmain body 326 between its upper and lower portions. Primary passage 326c is open at a first, lower end and terminates at a second, upper endhaving a reduced diameter valve retention aperture 326 d and a pluralityof smaller valve passages 326 f radially disposed thereabout, eachpassing through to valve seat 326 e. A drain groove 326 g is disposedabout valve seat 326 e within enter cavity 326 p and lies below thesurface of valve seat 326 e. One or more drain passageways 326 h providefluid communication between drain groove 326 g, and consequently centercavity 326 p, and the exterior of main body 326. When vent assembly 325is installed in threaded port 322 cc of main housing 322, an O-ring (notshown) is utilized to insure a proper seal, and an appropriate tool isused to engage tool form 326 a to first turn down main body 326 to anappropriate torque. As illustrated, tool form 326 a is an externalhex-form, such that an open wrench or socket may be used to install mainbody 326. Other specialized tool forms and corresponding tools arecontemplated within the scope of this application, including an internalhex-form such that a key wrench may be applied to install main body 326.

A flexible umbrella valve 327 is disposed in valve retention aperture326 d such that its retention bead 327 a lies within primary passage 326c and its sealing flange engages valve seat 326 e to close off theplurality of valve passages 326 f. The pressure rating of the particularumbrella valve 327 utilized can be selected to prevent shaft sealleakage and meet the requirements of the specific application to whichtransaxle 320 is applied. As case pressure in transaxle 320 builds withincreasing temperature during operation and reaches a value in excess ofthe pressure rating of umbrella valve 327, sealing flange 327 b islifted off of valve seat 326 e, opening valve passages 326 f toatmospheric pressure and allowing air, and in extreme cases hydraulicfluid, to be vented though valve passages 326 f.

Vent cap 328 is snapped onto main body 326 after installation ofumbrella valve 327 in valve retention aperture 326 d to complete theinstallation of vent assembly 325. Locking groove 328 a engages theperiphery of downwardly sloped flange 326 i to loosely join thecomponents of vent assembly 325, permitting the passage of air andliquids, such as water or hydraulic fluid, therebetween. As assembled,spray shield 328 b surrounds tool form 326 a to form a baffle to thwartintrusion of water or other fluids. In the event that intrusive waterdoes reach center cavity 326 p, it will collect in drain groove 326 g,pass through drain passages 326 h, follow along downwardly slopingflange 326 i and then proceed out of the vent assembly 325 between theloose engagement of flange 326 i and locking groove 328 a. The releaseof air and/or hydraulic fluid by umbrella valve 327 will result in thedischarge of the respective fluids from vent assembly 325 by means ofthe same pathway described for the drainage of water from vent assembly325.

An additional embodiment of a vent assembly 525 that may be utilizedwith a transaxle, such as transaxle 320, is illustrated in FIGS. 17, 18,19, and 20. Like vent assembly 325, vent assembly 525 comprises a mainbody 526, a valve 527, and a vent cap 528. Vent assembly 525, however,benefits from an expanded internal volume that acts as a catch basin forhydraulic fluid and hinders its discharge through valve 527. Ventassembly 525 also benefits from having its tool form 528 a disposed onthe external surface of vent cap 528 such that vent assembly 525 can bepreassembled prior to installation on a transaxle. Though shown as ahex-form, tool form 528 a can be formed in a variety of shapes tocooperated with known tools.

Main body 526 is formed as a basin-shaped fitting having an externallythreaded cylindrical lower section 526 b disposed about a primarypassage 526 c open at a first, lower end. Primary passage 526 c opens ata second, upper end into a circular basin 526 g having a floor 526 qthat slopes down to primary passage 526 c for drainage purposes and asidewall 526 r. Passing through sidewall 526 r are a valve retentionaperture 526 d and a pair of valve passages 526 f positioned proximateto, and above, valve retention aperture 526 d. A flexible umbrella valve527 is mounted in valve retention aperture 526 d in the mannerpreviously described for umbrella valve 327, selectively sealing valvepassages 526 f at a valve seat 526 e formed on the external surface ofsidewall 526 r. A spray guard 526 i formed external to sidewall 526 rjust below valve retention aperture 526 d cooperates with a spray guardprotrusion 528 c formed internal to vent cap 528 to protect umbrellavalve 527 from water intrusion. Concentrically positioned atop sidewall526 r is a chamfer 526 j that cooperates with a cylindrical wall 528 binternal to vent cap 528 to capture an O-ring 539, sealing the jointtherebetween. Rising from the floor 526 q of basin 526 g andconcentrically positioned about the second, upper end of primary passage526 c is a central tower 526 a having a plurality of anti-rotation slots526 m that engage cooperating anti-rotation ribs 528 e internal to ventcap 528. Basin passage 526 h through central tower 526 a permitscommunication between basin 526 g and primary passage 526 c. A pluralityof alignment slots 526 k above chamfer 526 j cooperate with a likenumber of alignment ribs 528 d formed internal to vent cap 528 tocorrectly align main body 526 and vent cap 528 for joinder. A pluralityof snap-lock protrusions 526 n along the external periphery of main body526 engage a like number of snap-lock ramps 528 f formed along theinternal periphery of vent cap 528 to join the component parts of ventassembly 525.

Vent assembly 525 performs in the manner previously described for ventassembly 325 as temperatures rise during operating conditions,permitting the venting of expanding air to atmosphere through valvepassages 526 f and the intervening space between main body 526 and ventcap 528, while improving the retention of hydraulic fluid expelled fromthe housing of a transaxle by means of basin 526 g and its communicationwith primary passage 526 c via basin passage 526 h.

FIGS. 21 through 27 depict an embodiment of a hydrostatic transaxle 420that primarily varies from the previously disclosed embodiments in thatits transmission 421 drives both a left-side axle 482L and a right-sideaxle 482R through a differential assembly 490. Correspondingly, mainhousing 419 comprises a left-side axle horn 419 a and a right-side axlehorn 419 b to provide rotational support for axles 482L, 4828,respectively, in the manner previously described for axle horns 122 a,322 a. Main housing 419 is sealingly closed by housing cover 323 with aplurality of fasteners 324 and integral locating pins 419 x as describedfor the joinder of main housing 322 and housing cover 323.

It will be understood that transmission 421 is substantially similar inform and function to transmission 321, and as such, will not be furtherdetailed herein. Any revisions to the pump thrust bearing grade or anyaddition of a valve plate to the pump running surface to accommodatehigher system pressures attendant with two-axle transaxles will beunderstood to lie within the scope of this disclosure. Similarly, thoughtransmission 421 is shown as incorporating filter assembly 356, it willbe understood that an alternate filter assembly, such as filter assembly556 may be considered within the scope of this disclosure. But for theincorporation of a differential-accommodating final drive gear or bullgear 491, reduction gear set 480 may also be considered substantiallysimilar in form and function to reduction gear sets 180, 380, and assuch, will not be further detailed herein. Any revisions to the specificgear reduction ratios to limit hydraulic system pressures will beunderstood to lie within the scope of this disclosure.

FIGS. 23 through 27 detail differential assembly 490 and its assembly.Generally speaking, differential assembly 490 is a necessary addition toa two-axle transaxle driven by a single transmission, such asillustrated by transaxle 420 and transmission 421. During vehicle turns,the axle associated with the larger, outside turn radius must rotate ata greater rate than the axle associated with the smaller, inside turnradius. Differential assembly 490 permits this accommodation.

In general terms, differential assembly 490 comprises a pair of opposingplanet bevel gears 492 whose rotational axes are collinearly disposedand a pair of opposing axle bevel gears 494 whose rotational axes (andcorrespondingly, those of left-side axle 482L and right-side axle 482R)are collinearly disposed. The rotational axes of these gear setsintersect in a perpendicular orientation, as each planet bevel gear 492engages each axle bevel gear 494 in a quadrilateral engagement pattern.

Bull gear 491 has various openings 491 a, 491 b and recesses 491 c toaccommodate the components of differential assembly 490 in thisquadrilateral engagement pattern. Each of a pair of openings 491 a isconfigured to accept a pin 493 upon which a planet bevel gear 492 isrotationally supported, the pin having a flat end 493 a at each end,which when properly situated in opening 491 a, prevents its rotation.Each opening 491 a also accommodates the planet bevel gear 492 itselfand serves as the gear's thrust surface under load where each of theplanet bevel gears 492 and the axle bevel gears 494 tend to push outaxially, expanding the quadrilateral engagement pattern. Opening 491 baccepts the proximal ends 482 a of the axles 482L, 482R which providerotational support for bull gear 491. A pair of recesses 491 c disposedabout opening 491 b on the opposing faces of bull gear 491 provideaccommodation in the differential stack-up for a radial protrusion 494 aformed on the face of the axle bevel gears 494 to ensure retention of aC-clip 489 that retains axle bevel gear 494 on its respective axle 482L,482R.

FIGS. 25 through 27 depict the sequencing of assembly for differentialassembly 490. Each axle 482L, 482R is rotationally supported near itsproximal end 482 a by a rotational support opening 419 d formed in mainhousing 419. An optional bushing (not shown) may line rotational supportopening 419 d, depending on vehicle application. Adjacent to theproximal end 482 a of each axle 482L, 482R is a C-clip retaining groove482 b and a set of splines 482 c adapted to engage a corresponding setof splines formed on the interior of axle bevel gear 494. Axle bevelgear 494 is first slipped onto splines 482 c, after which C-clip 489 isinserted in C-clip retaining groove 482 b. Axles 482L, 482R are movedoutboard until each axle bevel gear 494 encounters an inner wall of mainhousing 419 adjacent to rotational support openings 419 d to providespace for insertion of bull gear 491 between axle bevel gears 494. Thiscorrespondingly locates C-clip 489 within a recess 494 b formed in theface of axle bevel gear 494 about which radial protrusion 494 a isdisposed, further ensuring that C-clip 489 will not become dislodgedfrom C-clip retaining groove 482 b. Next, bull gear 491, with planetbevel gears 492 and pins 493 installed, is inserted between axle bevelgears 494. Axles 482L, 482R are then moved inboard to produce a gearmesh between planet bevel gears 492 and axle bevel gears 494.Correspondingly, the radial protrusions 494 a of each axle bevel gear494L, 494R are located within the corresponding recesses 491 c formed onthe opposing faces of bull gear 491, but with appropriate tolerances, donot physically engage the recesses 491 c. As shown in FIG. 27, theproximal ends 482 a of axles 482L, 482R now reside within bull gearopening 491 b, to provide rotation support for bull gear 491 duringdifferential operation. A pair of axle spacers 484 are then insertedbetween axle bevel gears 494 and main housing 419 to set the stack-up ofdifferential assembly components. Each axle spacer 484 has a yoke 484 bdisposed about its respective axle 482L, 482R and a protrusion 484 athat is captured in an anti-rotation slot 419 e between a pair of axlespacer retention ribs 419 c. Each axle spacer yoke 484 b also serves asa thrust surface for its respective axle bevel gear 494 uponinstallation.

During straight-line operation of a vehicle equipped with transaxle 420and differential assembly 490, each axle 482L, 482R is rotated at thesame rate as bull gear 491 transfers rotational energy from reductiongear set 480 to each axle 482L, 482R through the stack-up of planetbevel gears 492 and axle bevel gears 494, where each axle bevel gear 494turns at the same rotational rate as bull gear 491. As a vehicleproceeds through a turn, the one of the axles making the larger radiusturn will rotate at a greater rotational rate than bull gear 491, whilethe other of the axles making the smaller radius turn will rotate at arate less than that of bull gear 491.

While one or more specific embodiments of the invention have beendescribed in detail, it will be appreciated by those skilled in the artthat various modifications, combinations of disclosed elements, andalternatives to those details could be developed in light of the overallteachings of the disclosure. Accordingly, the particular arrangementsdisclosed are meant to be illustrative only and not limiting as to thescope of the invention which is to be given the full breadth of anyappended claims and any equivalent thereof.

What is claimed is:
 1. A drive apparatus disposed in a housing, thedrive apparatus comprising: a center section located in the housing; apump running surface and a motor running surface formed on the centersection; a hydraulic pump disposed on the pump running surface; ahydraulic motor comprising a motor cylinder block disposed on the motorrunning surface and in fluid communication with the hydraulic pump; amotor output shaft drivingly engaged with the motor cylinder block; anda bypass mechanism at least partially disposed in the housing andcomprising a block-lift member moveably disposed adjacent the motorcylinder block, and a bypass actuation rod having a first end disposedadjacent the block-lift member, wherein rotation of the bypass actuationrod causes the block-lift member to contact the motor cylinder block inat least two separate places, thereby lifting the motor cylinder blockoff the motor running surface.
 2. The drive apparatus of claim 1,wherein the block-lift member comprises a first block-lift leg having afirst formed end disposed adjacent a first side of the motor runningsurface, a second block-lift leg having a second end disposed adjacent asecond side of the motor running surface, opposite the first side, and apivot rod connecting the first block-lift leg to the second block-liftleg.
 3. The drive apparatus of claim 2, wherein the bypass actuation rodcontacts the first block-lift leg of the block-lift member.
 4. The driveapparatus of claim 3, wherein the first end of the bypass actuation rodcomprises a cam section.
 5. The drive apparatus of claim 4, wherein thebypass actuation rod extends through the housing and has a bypass armintegrally formed therewith to rotate the bypass actuation rod, whereinthe bypass arm includes at least one rotation limit, and wherein the atleast one rotation limit is formed to maintain a supported relationbetween the cam section and a portion of the center section.
 6. Thedrive apparatus of claim 2, further comprising a pivot groove formed inthe center section, wherein the pivot rod of the block-lift member isrotatably disposed in the pivot groove.
 7. The drive apparatus of claim2, wherein the block-lift member further comprises a locating protrusionon the pivot rod shaped to engage a corresponding locating rib on thecenter section.
 8. The drive apparatus of claim 7, wherein the first endof the bypass actuation rod comprises a cam section and the cam sectionbears against the first formed end of the first block-lift leg to forcethe block-lift member to rotate about an axis of the pivot rod.
 9. Thedrive apparatus of claim 8, further comprising a retention projectionformed on each of the first end and the second end, wherein each of theretention projections interfaces with a corresponding arcuate surfaceformed on the center section to retain the pivot rod in a pivot grooveformed in the center section.
 10. The drive apparatus of claim 1,wherein the bypass actuation rod comprises an O-ring groove structuredto receive an O-ring, wherein the O-ring seals an opening for the bypassactuation rod formed in the housing and wherein the bypass actuation rodfurther includes a locking tab structured to retain the bypass actuationrod in the housing.
 11. A drive apparatus, comprising: a hydrauliccylinder block rotatably disposed on a running surface in a housing andin fluid communication with a hydraulic porting system, the hydrauliccylinder block drivingly engaged to a shaft; and a block-lift memberdisposed adjacent to the running surface and comprising a firstblock-lift leg having a first end disposed adjacent a first side of therunning surface, a second block-lift leg having a second end disposedadjacent a second side of the running surface, opposite the first side,and a pivot rod connecting the first block-lift leg to the secondblock-lift leg; and a bypass actuation rod having a proximal enddisposed adjacent to the block-lift member and a distal end disposedexternal to the housing, wherein rotation of the bypass actuation rodcauses the block-lift member to contact the hydraulic cylinder block inat least two places, thereby lifting the hydraulic cylinder block offthe running surface to disengage the hydraulic cylinder block from thehydraulic porting system.
 12. The drive apparatus of claim 11, whereinthe block-lift member is U-shaped, and the first end of the bypassactuation rod comprises a cam section that contacts the first block-liftleg of the block-lift member.
 13. The drive apparatus of claim 11,wherein the bypass actuation rod extends through the housing and has abypass arm integrally formed therewith to rotate the bypass actuationrod, wherein the bypass arm includes at least one rotation limit. 14.The drive apparatus of claim 11, further comprising a first retentionprojection formed on the first end and a second retention projectionformed on the second end, wherein the first retention projectioninterfaces with a first arcuate surface formed adjacent to one side ofthe running surface, and the second retention projection interfaces witha second arcuate surface formed adjacent to a second side of the runningsurface.
 15. An axle driving apparatus, comprising: a housing; a centersection disposed in the housing and comprising a hydraulic portingsystem, a pump running surface and a motor running surface; an inputshaft extending into the housing and engaged to and driving a hydraulicpump disposed on the pump running surface; a motor cylinder blockdisposed on the motor running surface and in fluid communication withthe hydraulic pump through the hydraulic porting system; a motor outputshaft drivingly engaged with the motor cylinder block and engaged to areduction gear set disposed in the housing, the reduction gear setengaged to and driving a single output axle extending out one side ofthe housing; a block-lift member disposed adjacent to the motor runningsurface and comprising a first block-lift leg having a first enddisposed adjacent a first side of the motor running surface, a secondblock-lift leg having a second end disposed adjacent a second side ofthe motor running surface, opposite the first side, and a pivot rodconnecting the first block-lift leg to the second block-lift leg; and abypass actuation rod having a proximal end disposed adjacent to theblock-lift member and a distal end disposed external to the housing,wherein rotation of the bypass actuation rod causes the block-liftmember to contact the motor cylinder block in at least two places,thereby lifting the motor cylinder block off the motor running surfaceto disengage the motor cylinder block from the hydraulic porting system.16. The axle driving apparatus of claim 15, wherein the first end of thebypass actuation rod comprises a cam section.
 17. The axle drivingapparatus of claim 15, further comprising a pivot groove formed in thecenter section, wherein the pivot rod of the block-lift member isrotatably disposed in the pivot groove.
 18. The axle driving apparatusof claim 17, wherein the block-lift member further comprises a locatingprotrusion on the pivot rod shaped to engage a corresponding locatingrib on the center section.
 19. The axle driving apparatus of claim 15,wherein the block-lift member is U-shaped, and the first end of thebypass actuation rod comprises a cam section and the cam section bearsagainst the first end of the first block-lift leg to force theblock-lift member to rotate about an axis of the pivot rod.
 20. The axledriving apparatus of claim 19, further comprising a first retentionprojection formed on the first end and a second retention projectionformed on the second end, wherein the first retention projectioninterfaces with a first arcuate surface formed on the center section andthe second retention projection interfaces with a second arcuate surfaceformed on the center section.